Central Pacific El Niños and the North Pacific Oscillation: Toward A New Paradigm of Pacific Climate Variability

13 March 2015, 1:00 PM

Tropical and extratropical Pacific climate variability substantially impact physical and biological systems in the Pacific Ocean on interannual and decadal timescales. They are also integral elements of sensible weather patterns over North America and Eurasia on seasonal to decadal time scales. The current paradigm of Pacific climate variability centers around the three leading modes of variability in the atmosphere and ocean: the El Niño-­‐Southern Oscillation (ENSO), the Aleutian Low (AL), and the Pacific Decadal Oscillation (PDO). However, new studies now highlight the emerging roles of secondary modes of variability in the Pacific basin (i.e., Central Pacific El Niños or Warmings (CPWs), the North Pacific Oscillation (NPO), and the North Pacific Gyre Oscillation (NPGO)) in explaining and driving other aspects of the climate system.

This talk will focus on establishing the foundation of a new framework to include these secondary modes through better understanding of the forcing dynamics of the atmospheric component – the NPO. Through observations and model experiments, I will illustrate that the NPO itself exhibits sub-­‐seasonal and seasonal-­‐scale variability, but only its southern node (i.e., the one near Hawaii) contains substantial quasi-­‐decadal variability (7-­‐15 years). This periodicity of the subtropical node of the NPO mirrors that observed with the CPW phenomenon. By using a simple atmospheric general circulation model, I will show that forcing from sea surface temperature variability associated with CPWs drives a substantial fraction of the low-­‐frequency component of the southern node of the NPO. Finally, NPO variability directly integrates into the underlying North Pacific Ocean to form the characteristic NPGO pattern. This established framework (CPW-­‐NPO-­‐NPGO) together with the existing ENSO-­‐AL-­‐PDO framework provides added explanatory power to the overarching influence of Pacific climate variability on global climate. It also opens the door for several new research avenues into sub-­‐seasonal and seasonal forecasting and improving decadal-­‐scale climate projections, both of which have significant socioeconomic impacts.

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